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Clinical presentation

Respiratory distress predominates over esophageal symptoms, usually presenting early in the neonatal period.

Pathology

Aberrant left pulmonary arteries are thought to arise from a failure of formation of the 6th aortic arch. They have an anomalous origin from the posterior wall of the right pulmonary artery before coursing to the left lung passing posterior to the trachea and anterior to the esophagus.

The term “sling” is best used when the proximal portion of the anomalous vessel impinges on the right main bronchus and causes air trapping of the entire right lung, or right middle or lower lobes.

Radiographic features

Plain radiograph

Conventional radiographs obtained in neonates at birth may show fetal fluid retention or air, with a mediastinal shift usually to the left side.

In adults, a left-sided deviation of the trachea and an anterior bowing of the right main stem bronchus may be seen. In cases of ring sling complex, radiographs often show an absence of unilateral pulmonary aeration.

Fluoroscopy

In most instances, the barium oesophagogram characteristically shows a mass between the trachea and the esophagus just above the level of the carina, usually seen as an anterior indentation over the esophagus.

CT/MRI

The main bronchi have horizontal courses (i.e. low T-shaped carina), and vascular anatomy is normally well delineated on CT or MR angiography. Atelectasis may be seen in the upper lobes.

Treatment and prognosis

Repositioning of the artery usually reverses compression, particularly when the underlying tracheobronchial tree is normal.

The mortality rate is high in patients requiring tracheal reconstruction because the stenosis is primary and not due to the vessel.

The success of reconstructive procedures in the rigid trachea can be studied by using three-dimensional CT techniques such as virtual bronchoscopy.

Practical points

it is the only vascular ring to pass between the trachea and esophagus

it compresses tracheae posteriorly and causes anterior impression over the esophagus on lateral radiographs

References

1. Rings, Slings, and Other Things: Vascular Compression of the Infant Trachea Updated from the Midcentury to the Millennium—The Legacy of Robert E. Gross, MD, and Edward B. D. Neuhauser, MD1. Radiology 2000; 216:624–632